1. Field of the Invention
The present invention provides an improved method for the preparation of esters such as t-butyl acetate by reaction of a tertiary olefin with acetic acid in the presence of a large pore zeolite catalyst such as Zeolite Y, Zeolite X or Zeolite beta.
2. Description of the Prior Art
It is known to produce esters by the reaction of an olefin such as isobutylene with a lower carboxylic acid over a sulfonate group-containing cation exchange resin. See U.S. Pat. No. 3,678,099 and the references disclosed therein including U.S. Pat. Nos. 2,678,332, 3,031,495, 3,172,905 and 3,173,943.
A problem which is encountered in such prior procedures has been the tendency for polymerization of the olefin to occur during the esterification which results both in significant yield losses and in the formation of products such as olefin dimer which are difficult to separate from the product ester. For example, isobutylene dimer forms an azeotrope with t-butyl acetate thus making separation exceedingly difficult.
Problems of diisobutylene formation can be substantially overcome through the use of a selectivity enhancing modifier such as tertiary butanol. However, although the use of such a modifier has striking advantages, its use entails additional processing costs and purification procedures.
Other processes are described. For example, U.S. Pat. No. 3,492,341 describes the reaction of isobutylene with acetic acid to form ester using a mordenite aluminosilicate catalyst.
U.S. Pat. No. 4,365,084 describes ester production by reaction of a linear or slightly branched olefin with acetic acid using a catalyst such as HZSM-5. The use of olefins having unsaturation at the number 2 carbon atom is excluded.
U.S. Pat. No. 4,461,729 is similar to 4,365,084 and contains the additional step of hydrolyzing the ester to form secondary alcohol.
U.S. Pat. No. 4,465,852 relates to ester preparation by reaction of olefin with acetic acid. Although a great number of olefins are mentioned, including isobutylene, and a great number of catalysts are mentioned, including ZSM-5, the olefins exemplified are ethylene and propylene and the claims are limited to ethylene, propylene and butylene.
Copending patent application Ser. No. 09/022183, now U.S. Pat. No. 5,994,578 filed Feb. 11, 1998 describes ester preparation by reaction of an olefin such as isobutylene with acetic acid using a ZSM-5 catalyst. Data are presented indicating that at the reported conditions of the testing, poor results were achieved with large pore zeolite catalyst, Zeolite beta.